Computing & Information Sciences Kansas State University Monday, 17 Sep 2007CIS 560: Database System Concepts Lecture 12 of 42 Monday, 18 February 2008 William H. Hsu Department of Computing and Information Sciences, KSU KSOL course page: Course web site: Instructor home page: Reading for Next Class: Section 6.1 – 6.2, Silberschatz et al., 5 th edition Graphical Query by Example (GQBE), E-R Intro Notes: Relational Calculi, PS3

Computing & Information Sciences Kansas State University Monday, 17 Sep 2007CIS 560: Database System Concepts Query-by-Example (QBE) ‏ Basic Structure Queries on One Relation Queries on Several Relations The Condition Box The Result Relation Ordering the Display of Tuples Aggregate Operations Modification of the Database

Computing & Information Sciences Kansas State University Monday, 17 Sep 2007CIS 560: Database System Concepts QBE — Basic Structure A graphical query language which is based (roughly) on the domain relational calculus Two dimensional syntax – system creates templates of relations that are requested by users Queries are expressed “by example”

Computing & Information Sciences Kansas State University Monday, 17 Sep 2007CIS 560: Database System Concepts QBE Skeleton Tables for the Bank Example

Computing & Information Sciences Kansas State University Monday, 17 Sep 2007CIS 560: Database System Concepts QBE Skeleton Tables (Cont.) ‏

Computing & Information Sciences Kansas State University Monday, 17 Sep 2007CIS 560: Database System Concepts Queries on One Relation Find all loan numbers at the Perryridge branch. _x is a variable (optional; can be omitted in above query)‏ P. means print (display)‏ duplicates are removed by default To retain duplicates use P.ALL

Computing & Information Sciences Kansas State University Monday, 17 Sep 2007CIS 560: Database System Concepts Queries on One Relation (Cont.) ‏ Display full details of all loans P._x P._y P._z Method 1: Method 2: Shorthand notation

Computing & Information Sciences Kansas State University Monday, 17 Sep 2007CIS 560: Database System Concepts Queries on One Relation (Cont.) ‏ Find names of all branches that are not located in Brooklyn Find the loan number of all loans with a loan amount of more than $700

Computing & Information Sciences Kansas State University Monday, 17 Sep 2007CIS 560: Database System Concepts Queries on One Relation (Cont.) ‏ Find the loan numbers of all loans made jointly to Smith and Jones. Find all customers who live in the same city as Jones

Computing & Information Sciences Kansas State University Monday, 17 Sep 2007CIS 560: Database System Concepts Queries on Several Relations Find the names of all customers who have a loan from the Perryridge branch.

Computing & Information Sciences Kansas State University Monday, 17 Sep 2007CIS 560: Database System Concepts Queries on Several Relations (Cont.) ‏ Find the names of all customers who have both an account and a loan at the bank.

Computing & Information Sciences Kansas State University Monday, 17 Sep 2007CIS 560: Database System Concepts Negation in QBE Find the names of all customers who have an account at the bank, but do not have a loan from the bank. ¬ means “there does not exist”

Computing & Information Sciences Kansas State University Monday, 17 Sep 2007CIS 560: Database System Concepts Negation in QBE (Cont.) ‏ Find all customers who have at least two accounts. ¬ means “not equal to”

Computing & Information Sciences Kansas State University Monday, 17 Sep 2007CIS 560: Database System Concepts The Condition Box Allows the expression of constraints on domain variables that are either inconvenient or impossible to express within the skeleton tables. Complex conditions can be used in condition boxes Example: Find the loan numbers of all loans made to Smith, to Jones, or to both jointly

Computing & Information Sciences Kansas State University Monday, 17 Sep 2007CIS 560: Database System Concepts Condition Box (Cont.) ‏ QBE supports an interesting syntax for expressing alternative values

Computing & Information Sciences Kansas State University Monday, 17 Sep 2007CIS 560: Database System Concepts Condition Box (Cont.) ‏ Find all account numbers with a balance greater than $1,300 and less than $1,500 Find all account numbers with a balance greater than $1,300 and less than $2,000 but not exactly $1,500.

Computing & Information Sciences Kansas State University Monday, 17 Sep 2007CIS 560: Database System Concepts Condition Box (Cont.) ‏ Find all branches that have assets greater than those of at least one branch located in Brooklyn

Computing & Information Sciences Kansas State University Monday, 17 Sep 2007CIS 560: Database System Concepts The Result Relation Find the customer_name, account_number, and balance for all customers who have an account at the Perryridge branch.  We need to:  Join depositor and account.  Project customer_name, account_number and balance.  To accomplish this we:  Create a skeleton table, called result, with attributes customer_name, account_number, and balance.  Write the query.

Computing & Information Sciences Kansas State University Monday, 17 Sep 2007CIS 560: Database System Concepts The Result Relation (Cont.) ‏ The resulting query is:

Computing & Information Sciences Kansas State University Monday, 17 Sep 2007CIS 560: Database System Concepts Ordering the Display of Tuples AO = ascending order; DO = descending order. Example: list in ascending alphabetical order all customers who have an account at the bank When sorting on multiple attributes, the sorting order is specified by including with each sort operator (AO or DO) an integer surrounded by parentheses. Example: List all account numbers at the Perryridge branch in ascending alphabetic order with their respective account balances in descending order.

Computing & Information Sciences Kansas State University Monday, 17 Sep 2007CIS 560: Database System Concepts Aggregate Operations The aggregate operators are AVG, MAX, MIN, SUM, and CNT The above operators must be postfixed with “ALL” (e.g., SUM.ALL. or AVG.ALL._x) to ensure that duplicates are not eliminated. Example: Find the total balance of all the accounts maintained at the Perryridge branch.

Computing & Information Sciences Kansas State University Monday, 17 Sep 2007CIS 560: Database System Concepts Aggregate Operations (Cont.) ‏ UNQ is used to specify that we want to eliminate duplicates Find the total number of customers having an account at the bank.

Computing & Information Sciences Kansas State University Monday, 17 Sep 2007CIS 560: Database System Concepts Query Examples Find the average balance at each branch. The “G” in “P.G” is analogous to SQL’s group by construct The “ALL” in the “P.AVG.ALL” entry in the balance column ensures that all balances are considered To find the average account balance at only those branches where the average account balance is more than $1,200, we simply add the condition box:

Computing & Information Sciences Kansas State University Monday, 17 Sep 2007CIS 560: Database System Concepts Query Example Find all customers who have an account at all branches located in Brooklyn.  Approach: for each customer, find the number of branches in Brooklyn at which they have accounts, and compare with total number of branches in Brooklyn  QBE does not provide subquery functionality, so both above tasks have to be combined in a single query.  Can be done for this query, but there are queries that require subqueries and cannot always be expressed in QBE. In the query on the next page  CNT.UNQ.ALL._w specifies the number of distinct branches in Brooklyn. Note: The variable _w is not connected to other variables in the query  CNT.UNQ.ALL._z specifies the number of distinct branches in Brooklyn at which customer x has an account.

Computing & Information Sciences Kansas State University Monday, 17 Sep 2007CIS 560: Database System Concepts Query Example (Cont.) ‏

Computing & Information Sciences Kansas State University Monday, 17 Sep 2007CIS 560: Database System Concepts Modification of the Database – Deletion Deletion of tuples from a relation is expressed by use of a D. command. In the case where we delete information in only some of the columns, null values, specified by –, are inserted. Delete customer Smith Delete the branch_city value of the branch whose name is “Perryridge”.

Computing & Information Sciences Kansas State University Monday, 17 Sep 2007CIS 560: Database System Concepts Deletion Query Examples Delete all loans with a loan amount greater than $1300 and less than $1500.  For consistency, we have to delete information from loan and borrower tables

Computing & Information Sciences Kansas State University Monday, 17 Sep 2007CIS 560: Database System Concepts Deletion Query Examples (Cont.) ‏ Delete all accounts at branches located in Brooklyn.

Computing & Information Sciences Kansas State University Monday, 17 Sep 2007CIS 560: Database System Concepts Modification of the Database – Insertion Insertion is done by placing the I. operator in the query expression. Insert the fact that account A-9732 at the Perryridge branch has a balance of $700.

Computing & Information Sciences Kansas State University Monday, 17 Sep 2007CIS 560: Database System Concepts Modification of the Database – Insertion (Cont.) ‏ Provide as a gift for all loan customers of the Perryridge branch, a new $200 savings account for every loan account they have, with the loan number serving as the account number for the new savings account.

Computing & Information Sciences Kansas State University Monday, 17 Sep 2007CIS 560: Database System Concepts Modification of the Database – Updates Use the U. operator to change a value in a tuple without changing all values in the tuple. QBE does not allow users to update the primary key fields. Update the asset value of the Perryridge branch to $10,000,000. Increase all balances by 5 percent.

Computing & Information Sciences Kansas State University Monday, 17 Sep 2007CIS 560: Database System Concepts Microsoft Access QBE Microsoft Access supports a variant of QBE called Graphical Query By Example (GQBE)‏ GQBE differs from QBE in the following ways  Attributes of relations are listed vertically, one below the other, instead of horizontally  Instead of using variables, lines (links) between attributes are used to specify that their values should be the same.  Links are added automatically on the basis of attribute name, and the user can then add or delete links  By default, a link specifies an inner join, but can be modified to specify outer joins.  Conditions, values to be printed, as well as group by attributes are all specified together in a box called the design grid

Computing & Information Sciences Kansas State University Monday, 17 Sep 2007CIS 560: Database System Concepts An Example Query in Microsoft Access QBE Example query: Find the customer_name, account_number and balance for all accounts at the Perryridge branch

Computing & Information Sciences Kansas State University Monday, 17 Sep 2007CIS 560: Database System Concepts An Aggregation Query in Access QBE Find the name, street and city of all customers who have more than one account at the bank

Computing & Information Sciences Kansas State University Monday, 17 Sep 2007CIS 560: Database System Concepts Aggregation in Access QBE The row labeled Total specifies  which attributes are group by attributes  which attributes are to be aggregated upon (and the aggregate function).  For attributes that are neither group by nor aggregated, we can still specify conditions by selecting where in the Total row and listing the conditions below As in SQL, if group by is used, only group by attributes and aggregate results can be output

Computing & Information Sciences Kansas State University Chapter 6: Entity-Relationship Model Design Process Modeling Constraints E-R Diagram Design Issues Weak Entity Sets Extended E-R Features Design of the Bank Database Reduction to Relation Schemas Database Design UML

Computing & Information Sciences Kansas State University Modeling A database can be modeled as:  a collection of entities,  relationship among entities. An entity is an object that exists and is distinguishable from other objects.  Example: specific person, company, event, plant Entities have attributes  Example: people have names and addresses An entity set is a set of entities of the same type that share the same properties.  Example: set of all persons, companies, trees, holidays

Computing & Information Sciences Kansas State University Entity Sets customer and loan customer_id customer_ customer_ customer_ loan_ amount name street city number

Computing & Information Sciences Kansas State University Relationship Sets A relationship is an association among several entities Example: HayesdepositorA-102 customer entityrelationship setaccount entity A relationship set is a mathematical relation among n  2 entities, each taken from entity sets {(e 1, e 2, … e n ) | e 1  E 1, e 2  E 2, …, e n  E n } where (e 1, e 2, …, e n ) is a relationship  Example: (Hayes, A-102)  depositor

Computing & Information Sciences Kansas State University Relationship Set borrower